1. Field of the Invention
The present invention relates to a keyboard assembly which is applicable to an electronic musical instrument to provide a simulated touch response of an acoustic piano.
2. Prior Art
The acoustic piano provides an action mechanism which transmits a motion of key to a string. In general, reaction against depression of key is differed with respect to each of the keys of the acoustic piano; in other words, a key-touch response is differed with respect each of the keys. Specifically, the key-touch response becomes "heavy" as pitch of a key depressed becomes low, while the key-touch response becomes "light" as the pitch of the key depressed becomes high. Such difference in key-touch response is caused due to necessity of a physical structure in the action mechanism. Thus, a performer, who plays the acoustic piano, should increase depressing force made by his finger or hand when the performer depresses a key which belongs to a relatively-low pitch division in a keyboard of the acoustic piano. In contrast, the performer softens depressing force to a key which belongs to a relatively-high pitch division of the keyboard of the acoustic piano.
Next, "key scaling", which is accomplished in keyboard instruments such as the acoustic piano, will be explained. In the keyboard instrument, hammer heads are different from each other in size and hardness in accordance with lengths of strings. Specifically, a hammer head, which is provided for the relatively-low pitch division of the keyboard, is made "soft" by being wound by a relatively large felt, while a hammer head, which is provided for the relatively-high pitch division of the keyboard, is made "hard" by being wound by a relatively small felt. In addition, intensity of the spring, which is applied to the key, as well as weight of the key are different with respect to each of the keys. Those elements affect the key-touch response; and they affect determination in weight of the keys. In order to get an average weight for some of the keys, a member of lead material is put into a wood-made portion of the key. Thus, weight of the key, which belongs to the high-pitch division of the keyboard, is set at 50 gram; weight of the key, which belongs to an intermediate-pitch division of the keyboard, is set at 55 gram; and weight of the key, which belongs to the low-pitch division of the keyboard, is set at 60 gram. In short, the key scaling is performed on the reaction to the depression of key in such a way that the key-touch response is gradually lessened in a pitch-ascending order of the keys of the keyboard.
In the conventional keyboard assembly, the key scaling is tuned by adjusting a manner of winding the felt around the hammer head or by adjusting the weight of the member of lead material. However, such adjustment is hard to perform with accuracy. Therefore, it is difficult to perform a desired key scaling to key-touch responses with high precision.
In addition, the keyboard is designed to inevitably perform a key scaling to dynamic key-touch responses. Because each key provides a hammer or the like which has a specific mass; in other words, each key has different resistance to depression of key. Herein, the dynamic key-touch response can be defined as resistance to depression of key in a duration between a key-depression start timing and a key-depression end timing. In general, a person, who is familiar with a piano providing a mechanism performing a key scaling to key-touch responses, may fail to familiarize himself or herself with the keyboard of the electronic musical instrument which does not provide such mechanism. Hereinafter, the mechanism performing the key scaling to key-touch responses will be simply referred to as a "key-touch scaling mechanism".
Meanwhile, the acoustic piano has a complicated structure and requires high cost. Therefore, all of characteristics in structure of the acoustic piano cannot be directly applied to the electronic musical instrument which requires switch processing and the like. For example, the electronic musical instrument employs the keyboard which does not use the action mechanism of the acoustic piano but which uses key switches provided for the keys respectively. In some cases, mutually-slanted relationship is established between a line, which connects supporting points of the keys disposed in the keyboard, and a line which connects the key switches, wherein each key switch has a reversed-cup-like shape. This relationship may result in undesired occurrence of a key scaling to sounding-stroke positions of the keys. In other words, a sounding-stroke position of a key, which belongs to the low-pitch division of the keyboard, should be different from that of a key which belongs to the high-pitch division of the keyboard. In some case, the keyboard employs a two-make-contact-type touch-response switch which is located beneath the key at a certain position between a tip-edge portion and a supporting point of the key. In that case, a different distance, measured between the supporting point of the key and the touch-response switch, is set with respect to each of the keys. Hence, even if the finger depresses the key with same key-depression force (or at same key-depression speed), a keyboard switch output, given by depressing a key belonging to the low-pitch division, should be different from a keyboard switch output given by depressing a key belonging to the high-pitch division. Herein, the keyboard switch output is defined as time-difference information between the contacts of the touch-response switch which are respectively turned on when the key is depressed, wherein the time-difference information corresponds to the key-depression speed.
When performing the key scaling to key-touch responses, the conventional technology suffers from some disadvantages described above. For this reason, the conventional technology fails to think out the design of the keyboard assembly which is suitable for performing the key scaling to key-touch responses and which can be actually manufactured in a factory. And the design of the keyboard assembly should be made on the ground that manufacturing cost and assembling cost should be reduced as low as possible.
By the way, some proposals are made to manufacture the keyboard assembly for the electronic musical instrument providing the key-touch scaling mechanism. For example, key scaling is performed with respect to a distance between a supporting point of a hammer and a supporting point of a key in the keyboard assembly providing multiple hammers; key scaling is performed with respect to a distance between a tip-edge portion and a supporting point of a key; and key scaling is performed with respect to a distance between a supporting point of a key and a rubber switch. In the meantime, certain technology, by which same "touch pressure" (i.e., static reaction to a depression of key) is employed for both of white and black keys of the keyboard at their tip-edge portions, had been conventionally known. Herein, same touch response is set for each of the white key and black key by making an effecting point between the white key and its hammer different from an effecting point between the black key and its hammer.
Even the third proposal by which the key scaling is performed with respect to the distance between the supporting point of the key and the rubber switch suffers from the aforementioned disadvantages. In addition, the third proposal may result in complicated arrangement for the switches, complicated structure for wiring patterns, complicated structure for a substrate, complicated structure for a keyboard frame and complicated structure for a mechanism or member for fixing the switches, all of which will reduce productivity in manufacturing the keyboard assembly. Hence, this proposal does not work in practice.
Moreover, many proposals are made to manufacture a key-return spring in a comb-like structure which is formed as one member. In addition, some proposals are made to manufacture a multi-stage structure for a spring-terminating portion of a key and to use resin formation for a spring bearing.
The above-mentioned proposal, by which the key-return spring is manufactured in the comb-like structure, does not consider about the key scaling to key-touch responses. Further, such comb-like structure is disadvantageous because the key-return spring, after being used for a long period of time, may become wobbly; and such structure is disadvantageous because of low efficiency in equipping the keyboard assembly with the key-return spring. In addition, another proposal, by which the spring-terminating portion of the key is manufactured in the multi-stage structure and the spring bearing is formed using the resin material, is not made under the consideration of the key scaling by which the key-touch responses are altered between the keys belonging to the high-pitch division and low-pitch division respectively. Or this proposal may result in occurrence of noises by the spring; or this proposal may result in low efficiency in making the keyboard assembly.